This invention relates to a process for recovering ruthenium easily and in a satisfactory yield from a material sparingly soluble in water, acid solutions and basic solutions.
Metal electrodes comprising a substrate of a corrosion-resistant metal such as titanium, zirconium, tantalum or niobium coated with electro-conductive and corrosion-resistant ruthenium metal or compounds thereof have come into common use in recent years due to their superior chlorine overvoltage characteristics and dimensional stability as an anode. While the rate of consumption of such an electrode may be low, it is desirable to interrupt its use after a suitable length of service in an electrolytic cell and recoat the electrode in order to maintain the highest efficiency.
Since ruthenium is one of the most expensive of the platinum group elements due to its extremely limited availability, ruthenium contained in the coated layer removed from the substrate should be recovered and be reused.
For this purpose, ruthenium should be recovered in the form of metal or compound thereof, soluble either in water, an acid solution or a basic solution, because it is common practice to apply coating compositions in solution on to the substrate in manufacturing metal electrodes. If, for instance, some insoluble substance such as ruthenium dioxide is present in the coating composition, coarse grains are formed on the surface of the electrode which prevent formation of a strong, uniform coating layer of ruthenium oxide.
A prior art process for recovering platinum metals used in coating metal electrodes is described in Japanese patent publication No. 26967/71 relating to a process in which a used electrode coating is removed by electrolysis in a molten salt. However, the use of highly corrosive molten salts in said process necessitates the use of special materials for the electrode and the electrolytic cell. The electrolysis of molten salts also requires complicated design and operating technology as well as high installation and operating costs.
It is an object of this invention to provide a process for efficiently recovering ruthenium from a ruthenium-containing substance sparingly soluble in any of water, acid solutions and basic solutions by simple chemical procedures in combination with the use of inexpensive chemicals.
It is another object of this invention to provide a process for recovering ruthenium in the form of metal or a compound thereof, soluble either in water, an acid solution or a basic solution.
It is still another object of this invention to provide a process for efficiently recovering pure ruthenium or compounds thereof from a ruthenium-containing substance soluble in any of water, acid solutions and basic solutions and having impurities soluble in any of water, acid solutions and basic solutions by simple chemical procedure in combination with the use of inexpensive chemicals.
It is still another object of this invention to provide a process for recovering ruthenium by using simple chemical treatments and inexpensive chemicals without employing any special materials of construction or complicated design and operating technology.
Other objects and advantages of the present invention will become apparent to those skilled in the art from the following description and disclosure.